A significant agricultural commodity, corn (maize), is processed for several purposes, including industrial uses in addition to human and animal consumption. An increasingly important industrial use of corn is the production of ethanol which is in turn used, for example, as a fuel. Due to increased demands, ethanol production from corn is expected to rise rapidly, with projections indicating a doubling of production capacity within the next few years.
A widespread method of ethanol production utilizes the Dry Grind process and modified versions thereof; see FIGS. 1 and 2. Ethanol producers often prefer the Dry Grind process to an alternative method known as Wet Milling (FIG. 3) due to the simplicity, low initial capital investment, and lower operating costs associated with Dry Grind. The Dry Grind process is currently estimated to yield about 70% of the ethanol produced in the United States. These trends of increased ethanol production and acceptance of Dry Grind are forecasted to continue.
Corn can be described as comprising several components. The four main components include starch, also referred to as the carbohydrate or sugar component; protein; fat, also referred to as oil; and fiber. In the Dry Grind process, starch is converted to ethanol. First, the corn is ground into corn flour. Next, water is added to the corn flour, and the resulting slurry is treated in the presence of enzymes to convert the sugars to glucose. Glucose is fermented using yeast to produce crude ethanol. The crude ethanol-water mixture is treated by distillation, yielding purified ethanol.
From the distillation step, the solids or “grains” coming out of the distilling column are called Distillers Grains. The water component resulting from the distillation column is evaporated, and the resulting “solubles” are mixed with the Distillers Grains; this combination is conventionally known as Distillers Grains with Solubles. Alternatively, the Distillers Grains are not mixed with the Distillers Solubles. Finally, the Distillers Grains or Distillers Grains with Solubles are dried, generating Distillers Dried Grains (DDG) or Distillers Dried Grains with Solubles (DDGS). DDGS consist largely of corn minus the starch component; in other words, DDGS have the remaining components of protein, fat, fiber, and some unconverted starch. Physically, it is a solid powdery or aggregate material with color hues ranging from a bright golden yellow to brown.
Dry Grind processing in the ethanol production industry thus yield DDGS as a major byproduct. Directly correlating with the increase in ethanol production, the supply of DDGS as a commodity will likely increase proportionately. As a commodity, DDGS has constrained economic value. For example, the typically high fiber content of DDGS restricts its applicability as a feed product. DDGS is highly suitable as an animal feed for ruminant animals such as cattle which can naturally digest the fiber. Non-ruminant animals, however, are generally less able to digest high fiber DDGS. DDGS as commercially produced is also found to be variable in its nutrient composition such as protein, fat, fiber, ash, or starch content (see Belyea, 2004). This variability can diminish the value of DDGS when business consumers consider certain criteria, such as minimum protein and/or fat content proportions, for a feed product to be of importance.
Attempts have been made to improve processes and products of ethanol production from corn. See U.S. Pat. No. 6,254,914 by Singh et al., issued Jul. 3, 2001; United States Patent Applications 20030104587 by Verser et al., published Jun. 5, 2003; 20030180415 by Stiefel et al., published Sep. 25, 2003; and 20030232109 by Dawley et al., published Dec. 18, 2003.
In Singh, et al., 2002, the possibility of using air aspiration to remove fiber from DDGS was investigated. A kilogram sample of DDGS was placed on a 20-mesh screen and aspirated with an air jet at a pressure of approximately 2.8 atmospheres using a procedure similar to that of Eckhoff et al., 1996. The study showed limited success for aspiration in recovering fiber from DDGS and in recovering phytosterol compounds which are plant sterols that may be useful in lowering cholesterol levels. Aspirating DDGS samples produced by the dry-grind ethanol process did not yield an aspirated fraction that was significantly enriched in phytosterols. Aspiration of DDGS resulted in enrichment of oil and protein content and reduction of the neutral detergent fiber in the “residual” DDGS fraction (original DDGS after the removal of the aspirated fraction; note that terminology in Singh et al., 2002 may not necessarily correspond to present usage herein). The reduction in fiber content of this residual DDGS, however, was not found to be large enough to make a practical feedstuff for non-ruminants because the fiber levels were significantly above levels typically found in non-ruminant diets (Singh et al., 2002).
An invention that improves the economic value of grain products such as DDG or DDGS is highly desirable. DDGS can be improved by one or more of decreasing the fiber content, enriching the protein and/or fat content, and standardizing the nutrient content of the commodity. Reduction of the high fiber content can open up the use of DDG or DDGS as a feed product to non-ruminant animals and help maintain the supply and demand balance of the commodity. As a side benefit, a fiber-enriched product of the invention can itself contribute value to an ethanol production plant as an additional useful product of the DDGS processing and ultimately of corn. Some examples of valuable products potentially available from the fiber-enriched products include corn fiber gum and corn fiber oil. The phytosterol-containing oil in the corn fiber (corn fiber oil) has potential use as a natural low-density lipoprotein (LDL) lowering nutraceutical (see Moreau R A et al., 1999, Cereal Chemistry 76(3):449-451; Singh V et al., 2003, Cereal Chemistry 80(2):118-122). A fiber-enriched product can also be useful for dietary needs or as a laxative.
Ground corn flour is a major ingredient in diets for swine and poultry, which do not digest fiber very well. There exists a demand for a method of increasing the digestible energy of corn flour and thus increasing value of corn flour as an ingredient in non-ruminant diets.
There also exists a demand for protein-rich grain products. The production of oilseeds, such as soybean and cottonseed in the U.S. was 93 million tons in 2008, an increase of 16% from 2007 (USDA-NASS, 2008). Most of the increased oilseed production was attributed to increased soybean production. Soybean meal, or SBM, is the material that remains after extracting oil from soybean flakes. Oil is extracted by either solvent extraction of ground flakes or by expeller process where the beans are heated and squeezed (SMIC, 2008). Soybean meal is considered a prominent source of plant protein for poultry diet. It has high protein content, and it is the highest in energy content of all common oil seeds. The demand for protein-rich products is increasing. The poultry industry uses a significant portion of U.S. soybean meal. There exists a need to increase the protein and energy contents in each pound of SBM. The high protein quality and consistency of nutrient content makes soybean meal a preferred choice over other feeds for poultry diets.
Cottonseed meal (CSM) is also produced after solvent extraction of oil from cottonseed kernels or by mechanical extraction; most cottonseed meal produced in the U.S. is produced by solvent extraction (SMIC, 2008). Soybean meal has 48% of protein, whereas cottonseed meal has 41%. With 41% of protein content, cottonseed meal is an excellent source of protein for a variety of animal species.
Wheat middlings (midds), a byproduct after extracting flour from wheat and durum during milling, are a useful feed for cattle (NDSU, 1999). Wheat middlings include screenings, bran, germ, shorts, offal and flour rejects. Crude protein content in wheat middling is typically 17% to 18% on a dry matter basis (NDSU, 1999).